I agree that any oil may leave the same sludge or varnish it just leaves the manufacturer an opening to deny a warranty. I went on a field trip with GM to a refinery in Casper Wyoming. That is where Goodwrench motor oil was bottled at the time. As the bottles came down a conveyor and were filled...
I agree that when forced into a repair the manufacturer would have to honor a warranty. As a service manager for several decades, I can tell you it runs much deeper than that. A dealer is only allotted a certain amount of warranty dollars. Most service managers also want to get the district...
I just got mine muddy and your right the wheel wells hold mud really well. I think I will spray mine with some trim spray with ceramic to see if that makes it easier to get clean.